The invention concerns a safety locking device for electromechanical equipment.
In many industrial fields, the machine components are actuated by an electric motor via a kinematic chain. In some applications, safety considerations make it necessary to lock the component or components in position when they are not being used.
To do this, it is known how to introduce an obstacle into a cavity produced in a rotating part of the kinematic chain, in order to cause a positive locking thereof. However, this makes it necessary to be able to stop the rotating part so that the cavity is in line with the obstacle, which is tricky to achieve. Moreover, under the effect of the release of the equipment or an attempt to operate it, the obstacle may be jammed in the cavity, which makes it difficult to withdraw it.
Motors are also known, equipped with a friction brake at the end of a shaft, in which a disc is integral with the motor shaft, whilst a second disc disposed opposite the first is able to move between a locking position in which it is pressed against the first disc with a view to locking the motor rotationally, and a release position in which the second disc is kept distant from the first disc, which allows free rotation of the motor. In general, the discs are held in one of the positions by the action of a resilient member, and in the other position by the constant action of an actuation member, for example an electromagnet, or a ram in which a chamber has been filled with oil and then closed off, acting counter to the resilient member.
In the event of failure of the actuation member (power supply failure with the electromagnet, or leakage in the case of the ram), the position which the actuation member made it possible to maintain is no longer guaranteed, and the locking device progressively slides towards the other position under the effect of the resilient means, which may prove dangerous. This is because the rotating shaft may be free to turn when it is deemed to be locked, or conversely the rotating shaft may be locked when it is deemed to be free to turn.
A few examples derived from the field of electric brakes for aircraft wheels will be given here. This type of brake comprises a stack of discs, some of which are able to move rotationally with the wheel (rotors), whilst the others, disposed in alternation with the first, are rotationally immobilised (stators). The brake comprises at least one electromechanical actuator provided with an electric motor and a mechanism arranged to press the discs with a view to generating a braking force on the wheel.
In order to immobilise the aircraft at rest, it is known how to keep the brake discs pressed, so that the wheel is locked in safety. To do this, in the context of an electric brake, it is advantageous to provide a means of locking the actuator, so that it suffices to actuate the actuator so that it presses the disc, and then to lock the actuator in this position by virtue of the locking means.
The use in this case of a system with an obstacle and a homologous cavity as a locking means is not satisfactory. This is because, when the aircraft is immobilised, the latter in general has just landed and therefore braked in a sustained fashion and the structure of the brake has therefore expanded under the effect of heat.
If the actuator is locked before the brake has cooled, the progressive contraction of the brake structure will result in increasing the pressing force on the discs. As a reaction, if the actuator is reversible, this increase in force may result in a jamming of the obstacle in the cavity which receives it, which may give rise to difficulties in releasing the finger.
Moreover, it is necessary to size the obstacle generously in order to prevent it breaking during an attempt to activate the actuator locked by the obstacle.
Likewise, the use of a friction disc system for locking the actuator is also not satisfactory. Such a system is certainly more tolerant to internal or external forces which tend to force the locking (for example an attempt to actuate the actuator whilst the locking system has been put in the locking position), but does not guarantee a high level of security.
This is because the actuator in general comprises an actuation member arranged so as to keep the friction discs of the actuator in a separated position when the actuator is active (and therefore electrically supplied), a spring pressing the discs against each other when the actuation member is not supplied in order to lock the actuator. A failure in power supply to the actuation member (or a failure in functioning thereof) would result in locking the actuator in an unwanted fashion in the position which it occupies at the time of the incident, making it inoperative.
There is also known, from the document U.S. Pat. No. 5,949,168, a brake for a motor vehicle with a locking device comprising a manoeuvring member used solely to make the locking device change from a release position to a locking position. The release position is held by means of a spring, whilst the locking position is held by means of a rotation of the motor in a direction tending to press the brake disc, having the effect of putting the locking device in irreversible jamming.
The locking device presented in this document is designed to allow automatic unjamming of the locking device under the effect of a rotation in the opposite direction to the motor, which puts the locking device back in the release position.
Such a system cannot be used in aeronautics just as it is, a field in which it is not desirable for an accidental rotation of the motor, whilst the locking device is in the locking position, to result in the release of the motor, and therefore in the release of the brake, which could prove dangerous.
The invention therefore aims to propose a safety locking device for electromechanical equipment, not requiring the continuous action of an actuation member for keeping the device in one or other of the locking or release positions, whilst being tolerant to an internal or external force which would tend to force the locking, without this force being able to change the locking device from the locked state to the free state.
The object of the invention is more precisely a safety locking device intended to equip electromechanical equipment which is provided with a shaft rotating about a rotation axis, the device comprising a first friction element rotationally connected to the said shaft and extending in a plane normal to the rotation axis of the said shaft, and a second friction element immobile with respect to rotation and extending opposite the first friction element, one of the two friction elements being able to move in translation along the said axis, under the action of controllable actuation means, between a locking position in which the two friction elements are pressed against one another by a resilient member and a release position in which the two friction elements are kept separated, the said actuation means not participating in the maintenance of one or other of the locking or release positions. According to the invention, the locking and release positions correspond to successive angular positions of a selector able to move in rotation and connected in translation to the friction element able to move in translation, the said selector being maintained in any one of its angular positions by the aforementioned resilient member, the controllable actuation means being arranged to provide the passage of the selector from one angular position to the following, and subsequently the passage of the friction element able to move in translation from one to the other of its locking and release positions.
Thus, the actuation means not being used to maintain one of the locking or release positions, they therefore no longer have to be supplied with power in a prolonged fashion in order to maintain the friction elements in one or other of their positions. Moreover, the use of friction elements, preferably with a positive obstacle, allows sliding under the effect for example of an attempt to activate the electromechanical equipment, or in the case of unwanted increase in the external force applied to the actuator.
In addition, the two positions are held by the resilient member, and an accidental rotation of the motor does not have the effect of causing the device to pass from the locking position to the release position.
It should be noted then that in the document U.S. Pat. No. 5,949,168 the locking and release positions correspond to alternate angular positions, the locking and release positions of the locking device according to the invention correspond to successive angular positions.
According to a preferred arrangement, the selector comprises a locating member which is received in hollows in a ring, the hollows being disposed circumferentially on the ring and being organised in a first and second series of alternating hollows, the hollows in the first series having a depth such that the friction elements are in contact before the locating member abuts on the bottom of the said hollows, and the hollows in the second series having a depth such that the locating member abuts on the bottom of the said hollows before the friction elements are in contact.
The locking and release positions are then simply obtained by placing the locating member in one or other of the series of hollows in the ring.
Advantageously, the controllable actuation means comprise a pusher which is able to move axially and which is arranged to push the selector counter to the elastic member so as to release the locating member from the hollow in the ring in which it is engaged, the selector and/or the pusher having a cam profile which causes a rotation of the said selector so as to cause the movement of the locating member towards an adjacent hollow when the said pusher returns to its initial position.
Thus, by a simple translation movement of the pusher which can easily be controlled, the concomitant rotation of the selector is brought about.
According to an advantageous arrangement, the cam profile is carried by the pusher and acts on the free end of the locating member.
According to a particular embodiment, the locating member comprises a plurality of teeth extending towards the ring, the teeth being in number half the number of hollows in the ring.
Advantageously, an additional return member cooperates with the pusher in order to return the latter to its initial position after its actuation.
The controllable actuation means preferably comprise an electromagnet serving to actuate the pusher, the said electromagnet being powered only to pass from a locking position to a release position of the friction element able to move in translation, or vice-versa.
Another object of the invention is a brake for an aircraft wheel, comprising a stack of discs comprising rotors connected with respect to rotation to the wheel, and stators fixed with respect to rotation and arranged in alternation in the stack with the rotors, the said brake comprising at least one electromechanical actuator arranged to press the stack of discs with a view to exerting an electromechanical braking force on the wheel. According to the invention, the electromechanical actuator is equipped with a safety locking device having at least one of the aforementioned characteristics, associated with a rotating shaft of the kinematic chain of the said actuator.